So my first tip from the trench is this:
Have a disignated room (when possible) for birthday slumber parties.
(This also aids in decorating for a color theme. It's mostly purple here, in case that was hard to tell.)
Seriously. My in-laws lived with us for a while, and when they moved out, hubby and I moved into their old room, and repurposed our old room (which also housed the bathroom) as a schoolroom (for homeschooling my 8yo)/playroom/den/slumber party room. Whereas homeschooling hasn't found its purpose there as much I'd like so far (due to it not being ready, and a lack of curriculum), the slumber party idea is going mahvelously.
My newly-eight-years-matured daughter only has two little friends here, so it's not as loud as it might be, but honestly, with them having their own room, I'm anticipating a relatively quiet evening. I'm not joking. I'm at my computer with a cup of coffee, my 13yo is in the kitchen doing her homework, the pizzas are cycling through the oven, and there's an episode of Psych on.
So far I'm not regretting my decision. But a lot of people have said they're praying for me tonight, so I believe that has a lot to do with it.
And - maybe most importantly - it will keep your 13yo from complaining all night about being "stuck with 8 year olds," when she couldn't find a friend's house to sleep over.